Objectives To investigate the influence of prenatal conditions on the development of immune responses. Last year we extended prior studies demonstrating that prenatal conditions can influence the development and expression of immune responses in the young rhesus monkey. Monkeys from two prenatal conditions were evaluated to assess several cellular immune responses, antibody responses against Haemophilus influenzae, and the monkeys' ability to contain infection with an attenuated strain of Salmonella typhimurium. Monkeys derived from a disturbed prenatal condition differed on several of the in vitro immune measures, including mixed lymphocyte responses and cytolytic activity, and were unable to contain and clear the bacterial infection as readily as control subjects. These studies confirm that relatively benign disturbances of pregnancy physiology can have long-lasting effects on the physical well-being of the fetus and infant. Key words prenatal, infancy, immunity, Haemophilus influenzae, Salmonella